For example, an image forming apparatus using electrophotographic system uniformly charges a photosensitive body surface (a scan object), scans the photosensitive body surface with light flux, and forms an electrostatic latent image at the photosensitive body surface. Then, the image forming apparatus develops the electrostatic latent image on the photosensitive body surface with toner to form a toner image on the photosensitive body surface, and transfers the toner image from the photosensitive body to a recording paper sheet.
A light scanning device scans the photosensitive body surface with light flux. This light scanning device includes a light-emitting element such as a semiconductor laser, a polygonal mirror, a plurality of reflective mirrors, and a plurality of lenses such as an fθ lenses. The light-emitting element emits a light flux. The polygonal mirror and the plurality of reflective mirrors reflect the light flux. The plurality of lenses deflect the light flux. The light flux from the semiconductor laser is guided to the photosensitive body surface by an optical member such as the polygonal mirror, the reflective mirror, and the respective lenses. The photosensitive body surface is scanned with the light flux, thus an electrostatic latent image is formed on the photosensitive body surface.
With such light scanning device, if a light flux emitted from the light-emitting element is linearly polarized light, the light flux may contain many P polarized components with respect to the reflecting surfaces of the polygonal mirror and the reflective mirror, reflectivity of P polarization significantly changes according to an angle of incidence and a reflection angle of the light flux with respect to the reflecting surface. Accordingly, incident light quantity distribution of light flux at the photosensitive body surface may be unbalanced.
In the case where a light-emitting element with a plurality of light-emitting points that emits the respective light fluxes in linear polarization, a light-emitting element that emits a so-called multibeam, is used, rotation of the light-emitting element adjusts incident intervals of the respective light fluxes on the photosensitive body surface. However, the rotation of the light-emitting element changes a polarization direction (a vibrating direction of electric field) of the respective light fluxes in linear polarization. This may increases a ratio of the P polarized components of the respective light fluxes with respect to the reflecting surfaces of the polygonal mirror and the reflective mirror. This further increase unbalance of incident light quantity distributions of the respective light fluxes at the photosensitive body surface.
For example, Patent Literature 1 employs a light-emitting element that emits multibeam. Rotation of the light-emitting element changes polarization directions of the respective light fluxes in linear polarization and changes a ratio of S polarized component to P polarized components of the respective luminous fluxes via a surface of optical member. This adjusts the luminescence level of the respective light fluxes.
However, even here, this simply rotates the light-emitting element. Accordingly, the polarization direction of the light flux in linear polarization changes, and the ratio of the P polarized component of light flux with respect to the surface of the optical member may be increased. This cause incident light quantity distribution of light flux at the photosensitive body surface to be more unbalanced.